Advances in the development and improvements of the luminous flux of light-emitting devices such as solid-state semiconductor and organic light-emitting diodes (LEDs) have made these devices suitable for use in general illumination applications, including architectural, entertainment, and roadway lighting. Light-emitting diodes are becoming increasingly competitive with light sources such as incandescent, fluorescent, and high-intensity discharge lamps.
One of the problems in designing LED luminaires is the difficulty of evenly illuminating a surface upon which light is directed. For example, when a luminaire is positioned in the vicinity of an upper portion of the surface, it is difficult to illuminate the lower portion of the surface with a brightness that is comparable to that at the upper portion. This problem is likewise similar when the luminaire is positioned in the vicinity of the lower portion of the surface. Furthermore, with particular regard to LEDs, a further requirement is the need for effective colour mixing of the different colours of light emitted by varying types of LEDs, in order to produce a desired uniform colour of light, for example, white light.
U.S. Pat. No. 6,200,002 discloses a light source that includes an array of LEDs in each of a plurality colours such as red, green, and blue in the entrance aperture of a tubular reflector which has convex walls facing the optical axis and flares outward toward the exit aperture. Mixing of the colours of LEDs is defined as being promoted by utilizing a large number of small LEDs with the LEDs of each color being centered on the optical axis. In particular this patent is directed to the mixing of light from a plurality of LEDs, however, it does not address the issue relating to evenly illuminating a surface when the light source is positioned such that it is off set relative to the central region of the surface.
Furthermore, U.S. Pat. No. 6,547,416 discloses a light source that includes an array of LED components in each of a plurality of colors such as red, green, and blue in the entrance aperture of a tubular reflector which has an exit aperture, an optical axis extending between the apertures, and a reflective circumferential wall extending between the apertures to reflect and mix light from the array of LED components. It is defined that at least a portion of the circumferential wall of the reflector body has a polygonal cross-section taken normal to the optical axis, and at least a portion of the cross-section taken parallel to the optical axis includes segments of a curve joined one to the next to form a plurality of facets for reflecting light from the LED components to said exit aperture. This patent is directed to mixing the multiple colours of light in order to create a colour controlled spotlight. However, it does not address the issue relating to being capable of evenly illuminating a surface when the light source is positioned such that it is off set relative to the surface.
An optical device for use with a non-imaging light source is disclosed in U.S. Pat. No. 4,964,025. The optical device is an asymmetric reflecting cup to be used in automobile stop lights. The sides of the cup are different, wherein in cross section, each side contains a circular portion and two different parabolic portions. This configuration of the optical device enables the emission of light in a relatively narrow range of angles, with different horizontal and vertical ranges, such that observers may see the automobile. Again this patent does not address the issues relating to being capable of evenly illuminating a surface when a light source is positioned such that it is off set relative to the surface or mixing multiple colours of light.
U.S. Pat. No. 4,441,783 describes both symmetric and asymmetric compound parabolic concentrators to be used for navigational lights, wherein these lights provide a means for a vessel to be seen and not to illuminate a particular object. The patent describes two geometric configurations for projecting light, namely symmetrical and asymmetrical compound parabolic concentrators, each of which may be constructed as either a reflective cavity or a refractive dielectric, thereby providing four basic designs for achieving uniform luminous intensity over a sharply bounded horizontal arc of visibility, and also for achieving a desired vertical arc of visibility. This patent, however does not address any means for simultaneously mixing different colours of light to create a uniform colour.
In addition, U.S. Pat. No. 5,727,108 discloses a compound parabolic concentrator (CPC) which has a modified prismatic dielectric structure used as the reflecting surface of the CPC which acts as a refractive reflector. The light rays undergo a single reflection from the prismatic surface between the input aperture and the output aperture of the CPC. However, this patent does not address the issue relating to being capable of evenly illuminating a surface when the light source is positioned such that it is off set relative to the surface.
Therefore there is a need for a new optical device that is capable of both enabling substantially even illumination of a surface when the light source is off set relative to the central region of the surface, while additionally providing for a desired level of light mixing in order to generate a uniform colour of light from different coloured light sources.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.